A polymer electrolyte fuel cell, for example, is known as one of types of fuel cell which produce electrical power utilizing an electrochemical reaction between hydrogen and oxygen. The polymer electrolyte fuel cell includes a stack which is constituted from a plurality of stacked cells. The cells constituting the stack each include an anode (fuel electrode) and a cathode (air electrode), and a solid polymer electrolyte membrane having a sulfonic acid group as an ion exchange group is interposed between each anode and cathode.
A fuel gas containing a fuel gas (hydrogen-enriched reformed hydrogen obtained by reforming hydrogen gas or hydrocarbon) is supplied to the anode, while an oxygen-containing gas (oxidant gas), e.g., air, is supplied to the cathode as an oxidant. Upon the supply of the fuel gas to the anode, hydrogen contained in the fuel gas reacts with a catalyst in a catalyst layer which constitutes the anode, thereby producing hydrogen ions. The produced hydrogen ions pass through the solid polymer electrolyte membrane and electrically react with oxygen in the cathode. Electrical power is thus produced through the electrochemical reaction.
Meanwhile, in fuel cell systems, in an attempt to start a fuel cell system at a low temperature, if water from when the system last stopped still remains in a fuel cell, the remaining water freezes and may cause the system to be unable to start. Even if the system can be started, product water resulting from its own reaction may freeze and cause power generation to stop.
In light of such circumstances, it has been proposed that, in order to prevent product water resulting from an electrochemical reaction from freezing in a fuel cell, in an attempt to start a fuel cell system, when the internal temperature of the fuel cell is equal to or lower than 0 degrees, the drive of a coolant pump is stopped so as to prevent heat exchange between a coolant at a temperature equal to or lower than 0 degrees and the fuel cell, thereby ensuring an operation for raising the internal temperature of the fuel cell, so that the internal temperature rapidly rises to higher than 0 degrees (see JP2003-36874 A).